The present invention relates generally to electronic security systems such as electronic article security (EAS) or radio frequency identification tag (RFID) systems for detecting the presence of a security tag within a security zone adjacent to system antennas, and, more particularly, to an improved antenna system structure for such a system that is portable and provides a secondary feature of providing interchangeable indicia thereon for advertising and the like.
A variety of electronic article surveillance systems have been proposed and implemented to restrict the unauthorized removal of articles from a particular premises. One common form of this is the electronic article surveillance system which has come to be placed near the exits of retail establishments, libraries and the like. However, electronic article surveillance systems are also used for purposes of process and inventory control, to track articles as they pass through a particular system, among other applications.
Irrespective of the application involved, such electronic article surveillance systems generally operate upon a common principle. Articles to be monitored are provided with tags (of various different types) which contain a circuit (a resonant circuit) for reacting with an applied radio-frequency field. A transmitter and a transmitting antenna are provided to develop this applied field, and a receiver and a receiving antenna are provided to detect disturbances in the applied field. Such transmitting and receiving antennas are generally located at or around points of exit from such facilities to detect the security tag, and thus the article, as it transits through the exit point. If the active circuit of a tag is passed between the transmitting and receiving antennas (which are generally placed near the point of exit from a given premises), the applied field is affected in such fashion that a detectable event is produced within the receiver. This is then used to produce an appropriate alarm. Systems of this general type are available from manufacturers such as Checkpoint Systems, Inc., of Thorofare, N.J., among others.
Due to environmental and regulatory considerations, individual systems are generally effective over only a limited area in which a security tag attached to a protected article may be reliably detected. Such an area, typically referred to as a security zone, may generally be limited to about six feet in width. While many stores and libraries have only a single exit doorway of a size commensurate with such a six foot wide security zone, many other retail establishments have eight or ten exit doorways arranged side by side. Furthermore, large mall stores frequently have a generally wide open area or aisle of ten feet or more in width serving as a connection with the mall. Thus, in many such situations, a plurality of systems are required to fully protect exit/entrance points having a width greater than that which can be reliably protected by a single system.
In a large mall entryway that needs to be protected, it is likely that the store owner will not want to employ a traditional system installation which would include multiple, large, side-by-side “pedestal” antenna structures, due to aesthetic visual or marketing reasons. Such store owners would typically prefer an invisible system in which the antenna structure is mounted in the floor beneath the entryway, hung over the entryway or both. Additionally, store owners would often prefer a system that is nonpermanent to allow for the antennas to easily be placed in different locations, or a system that may be only used on a part-time basis, but may be deployed as needed and otherwise be hidden.
Numerous patents address EAS and RFID systems. For example, U.S. Pat. No. 6,271,756 (Davies, Jr. et al.) teaches a security tag detection and localization system for detecting a resonant security tag in a security zone and generating an alarm signal. The security zone has a plurality of detection zones and includes an antenna array for radiating interrogation signals and receiving response signals. The antenna array forms the upper boundary, the lower boundary or both the upper and lower boundaries of a security zone and extends horizontally across the width and length of the security zone. The antenna array comprises at least two antennas. The antennas forming the upper and lower boundaries are disposed side-by-side in a single horizontal plane with each antenna being electromagnetically coupled to one of the detection zones. The security tag detection and localization system also includes one or more EAS sensors for transmitting interrogation signals to the antenna array, receiving response signals from the antenna array, and generating an alarm signal. The security tag detection and localization system also includes an annunciator connected to each EAS sensor, for receiving the alarm signal and indicating a detection zone corresponding to the alarm signal.
It would be desirable to provide a portable system. However, to this point, any portable system would necessitate the use of a system that is large and cumbersome to carry due to the large size of the required antennas.
Finally, sheet antennas are also well known. For example, U.S. Pat. No. 6,369,773 (Kashiwagi et al.) depicts a sheet antenna which comprises a substrate sheet, a layer of antenna element composed of a conductive material and a carbon-containing layer. The carbon-containing layer antenna element are laminated on the substrate. Here, the primary use according to this patent is for automobile use. This patent teaches the use of various plastic sheets and films, including, for example, polyolefins such as polypropylene, polyesters such as polyethylene, etc. However, sheet antennas adaptable for use for surveillance gates are not known.
All references cited herein are incorporated herein by reference in their entireties.